1. Field of the Invention
The invention relates to a process of elimination of hidden faces for the synthesis of a three-dimensional wire image. Such an image is displayed on a two-dimensional display device, for example a cathode tube, and represents an object or a symbol apparently having three dimensions. The image consists of polygonal facets, some of which are partially or completely masked by facets closer to the observer, to give the impression of a third dimension. Each facet can be plotted on the screen either by illuminating its surface, the image is then called surface, or by illuminating only the edges of the facet, the image is then called wire or iron wire.
2. Discussion of Background
Conventionally, a wire image is displayed on a cathode tube by a direct beam, consisting in deflecting the electron beam only to scan the edges and edge segments which are to be illuminated, restarting all the calculations for each displayed image.
Synthesis of wire images is less common than synthesis of surface images, but it offers a considerable advantage when the display device is a cathode ray tube. Actually, the electron beam of this tube is deflected to scan only the edges of the image, which makes it possible to obtain a great brightness even if the image bas a very great resolution. The synthesis of wire images most commonly made is bidimensional. The three-dimensional synthesis poses the problem of eliminating edge parts that must be hidden to restore the three-dimensional appearance.